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Abstract:

The invention relates to a flexible strip (1) for a civil engineering
structure, that can extend longitudinally along a longitudinal axis and
comprises at least one optical fibre (20) enabling a structure to be
localised and measured in terms of deformation and/or temperature, where
said optical fibre (20) is essentially arranged along the longitudinal
axis and is surrounded by an at least partially reinforced thermoplastic
polymeric matrix of continuous reinforcement fibres (30), essentially
along the longitudinal axis, and where the mass quantity of continuous
reinforcement fibres extending essentially along the longitudinal axis,
WCF, is higher than, or equal to, ten times the mass quantity of optical
fibre(s), WOF. The invention also relates to metrology devices and
associated methods.

Claims:

1. A flexible strip having a longitudinal axis and intended for
installation in or on a civil engineering structure, the flexible strip
comprising at least one optical fibre to allow determining locations and
measurements of deformation and/or measurements of temperature for the
structure, said optical fibre being arranged substantially along the
longitudinal axis and being surrounded by a thermoplastic polymer matrix
that is at least partially reinforced, substantially along the
longitudinal axis, with continuous reinforcing fibres, the amount by
weight of continuous reinforcing fibres extending substantially along the
longitudinal axis, WCF, being greater than or equal to ten times the
amount by weight of optical fibre(s), WOF, said flexible strip comprising
at least one region where the polymer matrix comprises continuous
reinforcing fibres, distributed in a substantially uniform manner,
surrounded by a region of polymer matrix free of continuous reinforcing
fibre, said optical fibre being arranged within said at least one region
where the polymer matrix comprises continuous reinforcing fibres.

2-6. (canceled)

7. The flexible strip of claim 1, comprising a plurality of regions where
the polymer matrix comprises continuous reinforcing fibres and at least
one optical fibre, said regions being arranged parallel to each other in
the direction of the strip length, side by side in the direction of the
strip width, and being separated by regions of polymer matrix free of
continuous reinforcing fibre.

8. The flexible strip of claim 1, wherein at least one optical fibre is
arranged substantially parallel to the longitudinal axis of the flexible
strip.

9. The flexible strip of claim 1, wherein at least one optical fibre is
arranged about a direction substantially parallel to the longitudinal
axis of the flexible strip.

10. An array of flexible strips intended for installation in or on a
civil engineering structure, wherein the flexible strips are bonded
together, and wherein each flexible strip of the array comprises at least
one optical fibre to allow determining locations and measurements of
deformation and/or measurements of temperature for the structure, said
optical fibre being arranged substantially along a longitudinal axis of
said flexible strip and being surrounded by a thermoplastic polymer
matrix that is at least partially reinforced, substantially along the
longitudinal axis, with continuous reinforcing fibres, the amount by
weight of continuous reinforcing fibres extending substantially along the
longitudinal axis, WCF, being greater than or equal to ten times the
amount by weight of optical fibre(s), WOF, at least some of the flexible
strips comprising at least one region where the polymer matrix comprises
continuous reinforcing fibres, distributed in a substantially uniform
manner, surrounded by a region of polymer matrix free of continuous
reinforcing fibre, said optical fibre being arranged within said at least
one region where the polymer matrix comprises continuous reinforcing
fibres.

11. A device for determining locations and measurements of deformation
and/or measurements of temperature, comprising at least one flexible
strip and a measurement device connected to at least one optical fibre of
a flexible strip and capable of emitting light and measuring
characteristics of the light reflected, backscattered, or transmitted in
said optical fibre, wherein at least one of said flexible strips
comprises at least one optical fibre to allow determining locations and
measurements of deformation and/or measurements of temperature for the
structure, said optical fibre being arranged substantially along a
longitudinal axis of said flexible strip and being surrounded by a
thermoplastic polymer matrix that is at least partially reinforced,
substantially along the longitudinal axis, with continuous reinforcing
fibres, the amount by weight of continuous reinforcing fibres extending
substantially along the longitudinal axis, WCF, being greater than or
equal to ten times the amount by weight of optical fibre(s), WOF said
flexible strip comprising at least one region where the polymer matrix
comprises continuous reinforcing fibres, distributed in a substantially
uniform manner, surrounded by a region of polymer matrix free of
continuous reinforcing fibre, said optical fibre being arranged within
said at least one region where the polymer matrix comprises continuous
reinforcing fibres.

12-13. (canceled)

14. Method for determining locations and measurements of deformation
and/or measurements of temperature in or on a civil engineering
structure, the method comprising: emitting light into at least one
optical fibre of a measurement device; and measuring characteristics of
light reflected, backscattered, or transmitted in said at least one
optical fibre, wherein said device comprises at least one flexible strip,
at least one of said flexible strips comprising at least one optical
fibre to allow determining locations and measurements of deformation
and/or measurements of temperature for the structure, said optical fibre
being arranged substantially along a longitudinal axis of said flexible
strip and being surrounded by a thermoplastic polymer matrix that is at
least partially reinforced, substantially along the longitudinal axis,
with continuous reinforcing fibres, the amount by weight of continuous
reinforcing fibres extending substantially along the longitudinal axis,
WCF, being greater than or equal to ten times the amount by weight of
optical fibre(s), WOF, said flexible strip comprising at least one region
where the polymer matrix comprises continuous reinforcing fibres,
distributed in a substantially uniform manner, surrounded by a region of
polymer matrix free of continuous reinforcing fibre, said optical fibre
being arranged within said at least one region where the polymer matrix
comprises continuous reinforcing fibres.

15. (canceled)

16. The flexible strip of claim 9, wherein said at least one optical
fibre is arranged following a path in the form of a sine wave.

17. The array of claim 10, wherein each flexible of said at least some of
the flexible strips comprises a plurality of regions where the polymer
matrix comprises continuous reinforcing fibres and at least one optical
fibre, said regions being arranged parallel to each other in the
direction of the strip length, side by side in the direction of the strip
width, and being separated by regions of polymer matrix free of
continuous reinforcing fibre.

18. The array of claim 10, wherein, in said at least some of the flexible
strips, at least one optical fibre is arranged substantially parallel to
the longitudinal axis of the flexible strip.

19. The array of claim 10, wherein, in said at least some of the flexible
strips, at least one optical fibre is arranged about a direction
substantially parallel to the longitudinal axis of the flexible strip.

20. The array of claim 10, wherein the flexible strips are bonded
together by thermal welding.

21. The device of claim 11, wherein said flexible strip comprises a
plurality of regions where the polymer matrix comprises continuous
reinforcing fibres and at least one optical fibre, said regions being
arranged parallel to each other in the direction of the strip length,
side by side in the direction of the strip width, and being separated by
regions of polymer matrix free of continuous reinforcing fibre.

22. The device of claim 11, wherein at least one optical fibre is
arranged substantially parallel to the longitudinal axis of the flexible
strip.

23. The device of claim 11, wherein at least one optical fibre is
arranged about a direction substantially parallel to the longitudinal
axis of the flexible strip.

25. The device of claim 24, wherein the flexible strips are bonded
together by thermal welding.

26. The method of claim 14, wherein said flexible strip comprises a
plurality of regions where the polymer matrix comprises continuous
reinforcing fibres and at least one optical fibre, said regions being
arranged parallel to each other in the direction of the strip length,
side by side in the direction of the strip width, and being separated by
regions of polymer matrix free of continuous reinforcing fibre.

28. The method of claim 27, wherein the flexible strips are bonded
together by thermal welding.

Description:

[0001] The invention relates to a flexible strip comprising at least one
optical fibre for carrying out deformation and/or temperature
measurements in or on a civil engineering structure.

[0002] It aims in particular to locate and measure disruptions such as
deformations and/or temperature variations in or on civil engineering
structures. Such measurements are generally conducted over long periods
of time in order to determine, for example, whether the structure is
suffering damage and is at risk of deterioration; these tests or
measurements enable precautionary monitoring, particularly for predictive
maintenance.

[0003] In known prior art devices, optical fibres are placed in or on a
surface of a structure to be monitored, in order to obtain measurements
in situ. These optical fibres generally have a diameter of between 80 and
500 μm, and in particular about 150 μm, comprising a central
portion consisting of a core and cladding which are capable of allowing
light to propagate and at least one protective sheath.

[0004] However, the integration of such optical fibres in or on a civil
engineering structure does present disadvantages. These optical fibres
are fragile and can be damaged during placement or later on by the
stresses they are exposed to (shear stresses, undesired bending of the
fibre). In certain cases they may deteriorate over time, particularly in
"hostile" environments where there is a risk of penetration of water or
alkaline ions, for example followed by prolonged contact with such a
"hostile" environment.

[0005] An object of the invention is to propose a device which allows
determining locations and measurements of deformation and/or measurements
of temperature for a structure, i.e. a civil engineering structure or a
portion of a civil engineering structure, which prevents the above
disadvantages. Another object of the invention is to provide such a
device for a reasonable cost and to allow easy installation in the
structure.

[0006] The invention thus proposes a flexible strip that can extend
longitudinally along a longitudinal axis and is intended for installation
in or on a civil engineering structure, comprising at least one optical
fibre to allow determining locations and measurements of deformation
and/or measurements of temperature for the structure, said optical fibre
being arranged substantially along the longitudinal axis and being
surrounded by a thermoplastic polymer matrix that is at least partially
reinforced, substantially along the longitudinal axis, with continuous
reinforcing fibres, the amount by weight of continuous reinforcing fibres
extending substantially along the longitudinal axis, WCF, being greater
than or equal to ten times the amount by weight of optical fibre(s), WOF.

[0007] Note that said flexible strip may be substantially neutral
concerning the mechanical resistance of the civil engineering structure
or may contribute to a reinforcing role of this structure. However, the
material of the flexible strip is different from that of the major part
of the structure. The latter consists for example of earth, concrete, and
sealing materials.

[0008] Due to the flexible strip of the invention, the optical fibre or
fibres can be protected from the mechanical and physicochemical damage
cited above, and a suitable load transfer for measurements between the
structure (host environment) and the optical fibre(s) to determine
locations and measurements of deformation and/or measurements of
temperature for a structure can be assured.

[0009] "Strip" is understood to mean a part capable of extending
longitudinally, along a longitudinal axis, having a length that is very
significantly greater than the width perpendicular to the longitudinal
axis, and this width being very significantly greater than the thickness
(or height). As examples, the length of such a strip is at least one
meter, for example about 3 to 10 meters, or significantly greater than
that (tens to hundreds of meters, or even several kilometers); the width
is between 1 and 30 cm, for example between 5 and 10 cm; the thickness is
between 1 millimeter and several centimeters, for example between 2 and
10 mm.

[0010] As an example, such flexible strips may equip embankments, dikes,
or structures of mechanically stabilized or compacted earth. Such strips
may also be introduced into natural earth (by simple or directional drill
holes) and/or embedded in sealing materials (mortar, resin, or other
sealing material). Such strips may also be positioned on the surface of
metal or concrete structure elements, or even be directly integrated into
the concrete (elements of bridges, dams, aprons, etc.). They may also be
integrated into dams of roller-compacted concrete (RCC) during
construction. They may be placed in shallow trenches in the surface of
the natural earth, for example in a karst collapse hazard area or a major
landslide area.

[0011] "Very significantly superior" is understood to mean an amount that
is at least twice the amount to which it is being compared.

[0012] In one embodiment, the width of the strip is at least five times
greater than its thickness.

[0013] "Flexible strip" is understood to mean a strip capable of easily
deforming along its length. As an example, a strip is considered to be
flexible when it can be bent to a radius of curvature of 200 mm.

[0014] In one embodiment, a flexible strip can be bent to a radius of
curvature of 50 mm.

[0015] In one embodiment, the strip is produced as a very long length and
can be cut to form strips of the length desired for installation on or in
a structure. Because of its flexibility, a very long strip can be rolled
onto a spindle to form a spool or reel usable on-site. It is thus very
easy to displace the very long strip and unroll it, and possibly cut it
to the desired length, at the construction site for example.

[0016] The flexibility of this strip allows adapting it to the
irregularities which may be encountered on or in a structure, while
preserving the optical fibre(s) provided for performing the desired
measurements and comprised within said flexible strip. These
irregularities may, for example, be related to the shape of the
structure, the presence of structure components that could damage an
optical fibre, such as aggregate, reinforcing steel, gravel/sand present
in the compacted soil, component elements of sealing mortar, etc.

[0017] In addition, the inventors have observed that choosing a device in
the form of a strip, comprising at least one optical fibre, is
particularly advantageous for obtaining deformation measurements in a
structure, for example in an embankment, dike, or structure of reinforced
earth. In fact, the strip shape provides a good load transfer between the
environment (measurand) and the sensor, and depending on the case can
lead to an amplification of the measurand effects by increasing the
effective detection area.

[0018] The inventors have observed that the service life and load transfer
of a flexible strip, particularly when inserted into a structure, is very
significantly improved when the optical fibre (or fibres) is (are)
surrounded by a thermoplastic polymer matrix comprising continuous
reinforcing fibres extending substantially along the longitudinal axis of
the flexible strip. The inventors were able to determine that a
significant improvement to the behavior of such a flexible strip occurs
when the amount by weight of continuous reinforcing fibres extending
substantially along the longitudinal axis is greater than or equal to ten
times the amount by weight of optical fibre(s).

[0019] In the invention, an orientation "substantially along an axis" is
understood to mean an orientation of between +10° and -10°
relative to this axis, and in particular between +5° and
-5°. In one embodiment, the continuous reinforcing fibres extend
along the longitudinal axis of the flexible strip.

[0020] In one embodiment, the thermoplastic polymer matrix is chosen from
among the following list of matrices: polyethylene, polypropylene, PVC,
polyether.

[0021] The thermoplastic polymer matrix may also comprise elastomers.

[0022] In one embodiment, the continuous reinforcing fibres are polymer
fibres for which the matrix is chosen from among the following list of
matrices: polyester, polyamide, polyolefin.

[0023] In one embodiment, which may be combined with the above embodiment,
the continuous reinforcing fibres are chosen from among glass fibres,
aramid fibres, carbon fibres, fibres from fibre crops such as flax or
hemp fibres, and metal fibres. The continuous reinforcing fibres are
generally, but this is not limiting, assembled in the form of threads
comprising a plurality of fibres.

[0024] The continuous reinforcing fibres may be essentially arranged, or
exclusively arranged, to be parallel to each other and to follow the
direction of the strip axis. They may also be assembled into cord(s),
plait(s) or strand(s).

[0025] In one embodiment, the central portion of the optical fibre, which
is capable of allowing light to propagate, is mineral and more
particularly is based on silica.

[0026] In another embodiment, this central portion of the optical fibre is
organic ("POF", Plastic Optical Fibre).

[0027] In order to calculate the amount by weight, WOF, of the optical
fibre(s) in a flexible strip, the central portion (core and cladding) and
the protective sheath bonded to this central portion are taken into
consideration. The optical fibre may be covered by other protections,
particularly to form a cable, but the other protections are not taken
into account in calculating the WOF value. These other protections may
consist of a metal sheathing, or of various coverings, for example
consisting of cloth and/or organic layers. The entire assembly can be in
cable form.

[0028] The optical fibre used may be single-mode or multi-mode.

[0029] In one embodiment, the optical fibre comprises Bragg grating. In
another embodiment, the optical fibre is used directly without adding any
transducing element.

[0030] The optical fibre(s) of a flexible strip is (are) intended to be
connected to a measurement device able to emit light and measure
characteristics of the light reflected, backscattered, or transmitted in
the optical fibre.

[0032] A flexible strip of the invention, comprising at least one optical
fibre, may further have one or more of the following optional features,
individually or in any possible combination: [0033] the amount by
weight of continuous reinforcing fibres, WCF, extending substantially
along the longitudinal axis, is greater than or equal to fifty times the
amount by weight of optical fibre(s), WOF; [0034] the flexible strip
comprises at least one region in which the polymer matrix comprises
continuous reinforcing fibres, distributed in a substantially uniform
manner, surrounded by a region of polymer matrix free of continuous
reinforcing fibre; [0035] a region of the polymer matrix comprises
continuous reinforcing fibres, and is free of optical fibre, and this
region at least partially surrounds an optical fibre; [0036] at least one
optical fibre is arranged within a region where the polymer matrix
comprises continuous reinforcing fibres; [0037] at least one optical
fibre is placed in direct contact with the polymer matrix; [0038] at
least one optical fibre is arranged in a tube having its outer wall in
direct contact with the polymer matrix; it is possible for the same
optical fibre to have a portion of its length in direct contact with the
matrix and another portion of its length in a tube, and in this case
different portions of the same optical fibre may have different functions
(for example these portions respectively measure the elongation and
measure the temperature); [0039] the flexible strip comprises a plurality
of regions in which the polymer matrix comprises continuous reinforcing
fibres and at least one optical fibre, and these regions are arranged
parallel to each other in the direction of the strip length, side by side
in the direction of the strip width, and are separated by regions of
polymer matrix free of continuous reinforcing fibre; [0040] at least one
optical fibre is arranged substantially parallel to the longitudinal axis
of the flexible strip; [0041] at least one optical fibre is arranged
about a direction substantially parallel to the longitudinal axis of the
flexible strip, for example following a path in the form of a sine wave;
[0042] an optical fibre is covered by at least 0.1 mm of polymer matrix,
or even at least 0.5 mm of polymer matrix; [0043] at least one external
surface of the flexible strip has a degree of roughness or asperities
that are more or less pronounced, which allow optimizing the load
transfer between the host medium and said strip; [0044] at least one
outer edge of the flexible strip has a notched portion to optimize the
load transfer between the host medium and said strip.

[0045] The invention also relates to an array of flexible strips bonded
together, in particular by thermal welding, wherein the flexible strips
include the features of any one of the above embodiments. It is thus
possible to perform measurements in a two-dimensional space.

[0046] The invention also concerns a device for determining locations and
measurements of deformation and/or measurements of temperature,
comprising at least one flexible strip having the features of any one of
the above embodiments or an array of the above flexible strips and a
measurement device connected to at least one optical fibre of a flexible
strip and capable of emitting light and measuring characteristics of the
light reflected, backscattered, or transmitted in said optical fibre.

[0047] In one embodiment of said device, at least one flexible strip
comprises at least one optical fibre arranged in direct contact with the
polymer matrix, and this optical fibre is used to perform deformation
measurements.

[0048] In one embodiment of said device, at least one flexible strip
comprises at least one optical fibre arranged in a tube having its outer
wall in direct contact with the polymer matrix and this optical fibre is
used to perform temperature measurements.

[0049] The invention also relates to a method for determining locations
and measurements of deformation and/or measurements of temperature in or
on a civil engineering structure, which makes use of a device according
to any one of the above features, comprising a step of emitting light and
a step of measuring characteristics of the light reflected,
backscattered, or transmitted in at least one optical fibre.

[0050] In one embodiment of this method, at least one flexible strip
comprises at least one optical fibre arranged in direct contact with the
polymer matrix, said fiber being used to perform deformation
measurements, and at least one optical fibre arranged in a tube having
its outer wall in direct contact with the polymer matrix, said fibre
being used to perform temperature measurements, and the deformation
measurement and temperature measurement are performed at the same time.

[0051] In another embodiment of this method, at least one flexible strip
comprises at least one optical fibre arranged in direct contact with the
polymer matrix and at least one optical fibre arranged in a tube having
its outer wall in direct contact with the polymer matrix, and these two
optical fibres are used simultaneously to obtain interferometric
measurements.

[0052] The invention will be better understood by reading the following
description, provided solely as an example, and by referring to the
attached drawings in which:

[0053] FIGS. 1 and 2 are schematic perspective views of an embodiment of a
flexible strip of the invention;

[0054] FIGS. 3 to 5 are schematic views of a cross-section perpendicular
to the longitudinal axis of an embodiment of a flexible strip of the
invention;

[0055] FIGS. 6 and 7 are schematic perspective views of an embodiment of a
flexible strip of the invention;

[0056] FIGS. 8 and 9 are schematic views of a cross-section along the
width and longitudinal axis of an embodiment of a flexible strip of the
invention;

[0057] FIGS. 10a, b and c are schematic top views of an embodiment of a
flexible strip of the invention;

[0058]FIG. 11 is a schematic perspective view of an array of flexible
strips bonded to each other according to the invention.

[0059] For clarity, the various elements represented in the figures are
not necessarily to scale. Identical references correspond to identical
elements in these figures.

[0060]FIG. 1 shows a schematic perspective view of an embodiment of a
flexible strip 1 of the invention.

[0061] This flexible strip 1 comprises an optical fibre 20 arranged along
the longitudinal axis, perpendicular to the width L and to the thickness
(height) e of said flexible strip and surrounded by a thermoplastic
polymer matrix comprising continuous reinforcing fibres 30. These
continuous reinforcing fibres 30 are arranged in a region 10 forming a
channel in which the optical fibre 20 is placed. The region 10, of width
L1, is substantially arranged at the core of the strip 1 and is
surrounded by a region 40 of polymer matrix free of continuous
reinforcing fibre. In the case represented, the region 40 comprises two
lateral regions 41 situated on each side when considering the width of
the region 10 comprising the continuous reinforcing fibres and two
regions 42 situated on each side when considering the height of said
region 10. The flexible strip 1 represented comprises a main surface 70
extending width-wise and length-wise along the strip and an edge 80
extending height-wise and length-wise along said strip. In this example,
the surface 70 is substantially flat and uniform and the edge 80 is
rounded.

[0062] As an example:

[0063] L=20 mm

[0064] e=3 mm

[0065] L1=15 mm

[0066] WOF=330 dtex

[0067] (the unit "dtex" corresponds to g per 10,000 m)

[0068] WCF=150 000 dtex

[0069] WCF/WOF=450

[0070]FIG. 2 shows a schematic perspective view of a second embodiment of
a flexible strip 1 of the invention. This flexible strip comprises a
plurality of regions 10 forming channels in each of which is placed an
optical fibre 20. Two contiguous channels are separated by a wall 43 of
polymer matrix free of reinforcing fibres. The strip illustrated in FIG.
2 may be considered as corresponding to placing side by side a plurality
of "pseudo-strips" 50 of the type illustrated in FIG. 1.

[0071] As an example:

[0072] L (total width of the strip 1)=50 mm

[0073] e=4 mm

[0074] WOF=1 320 dtex

[0075] WCF=350 000 dtex

[0076] WCF/WOF=265

[0077] In another embodiment represented in a cross-section in FIG. 3, the
flexible strip 1 has a substantially rectangular cross-section, as do the
regions 10 forming the channels in each of which an optical fibre 20 is
placed. As an example, the thickness or height e2 of the region 42
between the region 10 forming the channel and the main surface 70 of the
strip is between 10 and 30% of the total thickness or height e of said
strip. An optical fibre 20 is situated at a distance el from the main
surface 70 of the strip. In the example represented, the optical fibre is
situated at the center of the strip.

[0078] In one embodiment, the thickness between the exterior of the
optical fibre and an external wall of the flexible strip of the
invention, for example the thickness el, is at least 0.1 mm of polymer
matrix (with or without continuous reinforcing fibre), or even at least
0.5 mm of said polymer matrix.

[0079] Advantageously, the flexible strips corresponding to FIGS. 1 to 3
may be rolled onto a spindle to form a construction spool or reel. In
these embodiments, it can be compactly wound with an upper main surface
70 in contact with a lower main surface 70.

[0080] FIGS. 4 and 5 represent cross-sectional views of other embodiments
of a flexible strip according to the invention, where the main surface is
not flat. These strips can, however, be rolled onto a spindle to form a
construction spool or reel, but in a less compact manner than with the
above embodiments.

[0081] In the embodiment represented in FIG. 4, optical fibres 20 are
arranged in a central portion 45 of the strip, in a polymer matrix free
of continuous reinforcing fibres, and there is a region 15 of polymer
matrix comprising continuous reinforcing fibres 30 on each side of the
central portion 45 comprising optical fibres 20. On each side of this
central portion 45, extending out in the direction of the width, are
wings 44 free of continuous reinforcing fibres and optical fibre. The
region 15 of polymer matrix comprising continuous reinforcing fibres is
covered by a layer 46 of polymer matrix free of continuous reinforcing
fibres. This region 15 ensures the mechanical resistance of the strip and
the dimensions of the wings 44 can be chosen to optimize the load
transfer between the flexible strip and the medium that surrounds it.

[0082] In one variant of the embodiment of FIG. 4, represented in FIG. 5,
optical fibres 20 are also arranged in the wings 44.

[0095] FIGS. 6 and 7 show schematic perspective views of embodiments of
the invention in which at least one optical fibre 20 is placed in a tube
60 where it is free of constraints. These embodiments are presented for
the case of a flexible strip configuration similar to the one in FIG. 1.
It goes without saying that these embodiments can have applications in
the other flexible strips described above, or in any other flexible strip
according to the invention. One will note that the fibre 20 arranged in a
tube 60 may be arranged in this tube for its entire length or for only a
portion of its length, the other portion possibly being integrally
connected to the polymer matrix. The "tubed" optical fibre, free of
constraints, may be integrated into a channel 10 (represented) or into a
region 41 of polymer matrix free of continuous reinforcing fibre (not
represented).

[0096] It should be noted that an optical fibre arranged in a tube is
essentially independent of the stresses applied to the flexible strip in
which it is located. Such an arrangement is particularly suitable for
conducting temperature measurements.

[0097] In the embodiment in FIG. 7, an optical fibre arranged in a tube 60
is associated with an optical fibre integrally connected to the polymer
matrix. Such a strip is particularly suitable for obtaining temperature
measurements, using the fibre free of constraints in the tube, and
deformation measurements simultaneously. Using the temperature
measurement, it is possible to correct the measurements for any
thermomechanical and thermo-optical deformations and thus to obtain
precise measurements of local deformations of essentially mechanical
origin.

[0098] It is also possible to obtain interferometric measurements with
these two optical fibres.

[0099] FIGS. 8 and 9 show schematic cross-sectional views along the width
and length of embodiments of flexible strips of the types illustrated in
FIG. 1, to show the paths of the fibre in the flexible strip. The region
10 is represented, in which an optical fibre 20 has been placed and in
which the polymer matrix comprises continuous reinforcing fibres,
bordered by the region 41 of polymer matrix free of continuous
reinforcing fibre.

[0100] In the example in FIG. 8, the optical fibre is arranged in a
direction parallel to the longitudinal axis of the flexible strip. In
this embodiment the optical fibre deforms longitudinally in a manner
substantially identical to the deformation of the flexible strip. This
configuration is preferably chosen for cases where slight deformations
are to be measured, for example less than 4%, or even less than 2%. In
fact, it is estimated that the deformation before an optical fibre breaks
is generally less than or equal to 4% in the case of optical fibres based
on silica.

[0101] In the example in FIG. 9, the optical fibre is arranged in a sine
wave traveling in a direction parallel to the longitudinal axis of the
flexible strip, with a wavelength LP. This embodiment can allow obtaining
measurements where the deformation of the flexible strip is greater than
the breaking point of the optical fiber. When the flexible strip
elongates, the optical fibre can initially elongate into a sine wave of
increasing wavelength LP, until it approaches a position substantially
parallel to the longitudinal axis of the flexible strip. It is thus
possible to increase significantly the range of measurement and to
measure deformations on the order of 10% to 20% for example.

[0102] FIGS. 10a to c represent schematic top views of embodiments of
flexible strips according to the invention. The different embodiments
presented offer possibilities for adjusting the load transfer between the
medium and the flexible strip.

[0103]FIG. 10a shows an embodiment where the main surface 71 of the
flexible strip has a low roughness. An average coefficient of friction
results between the medium and said flexible strip.

[0104]FIG. 10b shows an embodiment where the main surface 72 of the
flexible strip comprises significant roughness, for example obtained
using ridges 73 arranged laterally to the surface of said flexible strip.
An increased coefficient of friction is obtained between the medium and
said flexible strip in comparison to the configuration illustrated in
FIG. 10a.

[0105]FIG. 10c shows an embodiment where the flexible strip comprises a
central portion 75 extending longitudinally and two lateral portions of
variable width comprising a plurality of segments 76 arranged
continuously with and of the same material as the central portion 75. An
edge of such a flexible strip comprises rectilinear segments 82
circumscribing the central portion 75 and rectilinear segments 81
circumscribing the greatest width of the lateral portions. In the example
represented, the main surface 74 of the flexible strip is slightly rough.
The presence of the segments 76 very substantially increases the adhesion
between the medium and the strip, due to the distributed anchors, in
comparison to the configuration illustrated in FIG. 10a.

[0106] In general, the flexible strips of the invention may be
manufactured by extrusion using techniques known to a person skilled in
the art.

[0107]FIG. 11 schematically illustrates an embodiment of the invention
where a plurality of flexible strips 1 of the invention are arranged in
an array 2 and bonded to each other at their points of intersection. As
an example, it is possible to attach the flexible strips at the areas of
intersection 90 by thermal welding, for example bringing their surface to
temperatures of between 100 and 200° C.

[0108] It is thus possible to obtain a grid for dimensional measurement
for a structure and to obtain planar mapping of deformations and/or
temperatures.

[0109] The flexible strips described above can be connected to measurement
devices able to emit light and measure the characteristics of the light
reflected, backscattered, or transmitted in the optical fibre(s)
comprised in said flexible strips. These form devices which allow
determining locations and measurements of deformations and/or
temperatures, which can be installed in or on a structure.

[0110] It will be noted that the flexible strips can be arranged
horizontally or vertically or at an angle within the structure, depending
on requirements.

[0111] The invention is not limited to these types of embodiments and is
to be interpreted in a non-limiting manner, encompassing any equivalent
embodiment.